Anteromedian pair of promesonotal spines present; middle of ring of promesonotal spines smooth or with pair of low tumosities, lacking distinctly pointed spines or oblique carinae; scapes lacking erect setae or with a few very inconspicuous short setae; propodeal spines thin and straight, not stout and curved anteriorly. See also Kempf (1963), Mackay (1998).

Natural History

Kempf (1963) summarized the biology of this species as follows:

"Bionomics. - The ensuing data have been compiled from papers by Forel (1893):371-372, 1912:187), Wheeler (1907:773-774), Wheeler & Mann (1914:42), Eidmann (1936:85-86), Borgmeier (1937:248) and Weber (1946:128-129). The contribution by Eidmann is by far the most complete.

The small and sluggish workers when foraging carry dry leaves and caterpillar droppings back to their nest. The nesting sites are either in open fields and woods or even in moist gullies. The nest proper is in the soil. On the surface it is marked by craters of earth crumbs, measuring not more than 8 cm in diameter. These superficial structures stand out by their color which is different from that of the top soil, indicating that the nest cavities are at some depth. According to Bondar (Borgmeier, 1937) nest chambers have been dug out at a depth varying from 80 to 100 cm. In Colombia, Forel (1912) found a rather shapeless fungus-garden of this species at very little profundity.

A fact reported by many observers and confirmed by my own field experience is that usually a small area contains many craters of the same species, whereas neighboring areas have none at all. H. H. Smith (Forel, 1893) who first called attention to the phenomenon, suggested that the craters of a given area represent the entrances of just one common formicarium (as happens with goeldii during the mating season, according to Luederwaldt). This, however, has not as yet been established conclusively.

The nest cavity, measuring 4-5 cm in width to 2.5-3 cm in height, possesses a flat ceiling and an excavated bottom. From the ceiling without the support of a framework of plant rootlets hang narrow clusters or threads of fungus material. These threads, which are quite consistent, are made up of finely cut up leaf material connected by the mycelium. The fungus itself has not as yet been identified. Eidmann states that superficially it resembles that of Atta sexdens, whereas Forel (1912) glibly states that it is not Pholiota (Rizotes) gongylophora. Away from the nest chamber lead several fine and threadlike tunnels barely giving passage to the tiny workers. Eidmann (1936, fig. 4) gives a photograph of a nest chamber with the suspended fungus garden.

While collecting in Puerto Rico, Wheeler (1907:774) made several attempts at excavation of the fungus garden of M. smithi but succeeded only once. In moist red clay under a stone he found a small irregular chamber with about 30 ants. The fungus garden, a small mass of approximately 2 cc in volume, consisted of caterpillar droppings studded with bromatia that scarcely differed from those of Cyphomyrmex rimosus and allies, the only Attine ants known to cultivate a yeast. Wheeler's discordant observation poses an interesting problem, but also needs further confirmation.

According to Eidmann, the colonies are polygynous. At any rate he found several dealated queens in a single nest chamber. The same author proclaims a lestobiotic relationship between M. smithi and Atta sexdens because he found a great many nest chambers of the former between the cavities made by the latter. However, if any such relationship exists, it is not obligatory since M. smithi also occurs in areas where no sign of an Atta sp. could be discovered. Perhaps this association, of which no details are known, dissolves itself in the loose relationship of facultative synoecetes.

In southeastern Brazil M. smithi lives occasionally side by side with M. goeldii under the same ecological conditions. Kerr (1961) even found 3 males of the former in a swarm of 150 males of the latter species at Rio Claro, Sao Paulo State, Brazil. None of the smithi males attempted to mate with goeldii queens."

Fernández-Marín et al. (2005) made observations on the biology of M. smithii in Puerto Rico as follows (abstract):

The genus Mycocepurus is a phylogenetically basal attine ant, so studies of its biology may provide insight into the evolution of behaviours associated with fungus-growing that characterize the tribe Attini. Mycocepurus smithii from Puerto Rico produces sexual females from July to September, but no males were observed in 2 years of observations, confirming previous observations elsewhere. Colonies were founded between July and August and most nests were haplometrotic (85% of 74 nests). After excavating a tunnel and small chamber, a foundress queen inserted her fore wings into the ceiling and used the wing surfaces as a platform on which the incipient fungal garden was grown. Foundresses foraged for substrate to grow the fungus garden. Growth of incipient colonies was slow: the first workers emerged 2-5 months after colony founding and, after 8 months, colonies contained on average only a single worker.

In Costa Rica this species inhabits disturbed and otherwise open habitats. I collected workers emerging from a nest in soil, in a lawn in front of a house at Tortuguero, on the Atlantic coast. Ulrich Mueller similarly collected a nest at a coastal site near Limón. I also collected smithii in a small patch of riparian forest at Finca La Pacifica in Guanacaste Province. Workers were in a Winkler sample of sifted leaf litter, together with a worker of M. curvispinosus.

Mycocepurus smithii appears to be a form that favors synanthropic habitats, while the very similar species M. tardus inhabits more forested habitats.